Dexron was never ment to be a substitute for P/S fluid. I don't know how or why that ever came to be. If you're going to us something besides P/S fluid, and are just dying to use ATF, use Ford Type F. It's hydraulic fluid and that's what P/S pumps use.
Ford Type F has grit in it to make the clutches and the steels grab. Dexron does not does not have these friction modifiers.
Transmissions and power steering pumps are all hydraulic systems however transmission fluid will thicken up when it gets really cold.
Of course the friction of the transmission action causes heat so that isn't an issue in the winter. My guess is power steering fluid is thinner and maintains
a more consistent viscosity in all weather over the transmission fluid. I can't see how it hurts to use ATF in a power steering pump, but I sure wouldn't use Type F in it.
Tom















